In order to avoid the harmful effects of the studs, in particular their strong abrasive action on the surfacing of the ground surface itself and a significantly deteriorated road behaviour on a dry ground surface, tire manufacturers have provided different solutions which consist of modifying the formulation of rubber compositions themselves.
Thus, a proposal has been made, first of all, to incorporate solid particles of high hardness, such as, for example, silicon carbide (see, for example U.S. Pat. No. 3,878,147), some of which will come to the surface of the tread as the latter wears and thus come into contact with the ice. Such particles, capable of acting in fact as micro-studs on hard ice, by virtue of a well-known “claw” effect, remain relatively aggressive with regard to the ground surface; they are not well suited to rolling conditions on melting ice.
Other solutions have thus been proposed which consist in particular in incorporating water-soluble powders in the constituent composition of the tread. Such powders dissolve more or less on contact with the snow or the melting ice, which makes possible, on the one hand, the creation at the surface of the tire tread of porosities capable of improving the grip of the tread to the ground surface and, on the other hand, the creation of grooves which act as channels for discharging the liquid film created between the tire and the ground surface. Mention may be made, as examples of water-soluble powders, for example, of the use of cellulose powder, vinyl alcohol powder or starch powder (see for example, Patent Applications JP 3-159803, and JP 2002-211203).
In all these examples, the solubility at very low temperature and within a very short time of the powder used is an essential factor in the satisfactory operation of the tread. If the powder is not soluble under the conditions of use of the tire, the abovementioned functions (creation of microporosities and of channels for draining the water away) are not performed and the grip is not improved. Another known disadvantage of these solutions is that they can be highly disadvantageous to the reinforcing of the rubber composition (and thus to their wear resistance) or to their hysteresis (and thus to their rolling resistance).